• Journal of Biosystems Engineering
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• 제8권2호
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• pp.1-10
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• 1983

The resulting characteristics of vibrations show different patterns for the various oscillating mechanisms. These vibrations causes troublesome operation problems for the operators and sometimes for the machines. Furthermore, in some cases the practical usage of this oscillating mechanism is constrained by its mechanical conditions. In this study, a balanced oscillating tillage tool with triple blades having different acting area was designed. The horizontal and vertical oscillating accelerations and draft power requirement due to the various travel speeds, lift angles, amplitudes and oscillating frequencies were investigated in a laboratory soil bin with a soil having invariable properties. The results obtained are summarized as follows: 1. Overall, the horizontal acceleration decreased as the oscillating frequency and amplitude decreased. But the increase in travel speed caused the decrease horizontal acceleration. The blade with the lift angle of $30^{\circ}$ exhibited the lowest value of horizontal acceleration among the blades tested. 2. For the vertical acceleration, the fluctuating trend of oscillating acceleration was similar to the trend of the horizontal acceleration. 3. The draft power requirement decreased as the amplitude and oscillating frequency increased. But the increase in travel speed caused the increase in draft power requirement. The blade with the lift angle of $10^{\circ}$ showed the lowest value of draft power requirement among the blades tested.

• 대한치과보철학회지
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• 제8권1호
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• pp.65-71
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• 1968

저자(著者)는 성장(成長) 발육기(發育期)에 있는 한국인(韓國人)의 His' line과 전두기저선(前頭基底線) 안이평면(眼耳平面) 하악평면(下顎平面) 구개평면(口蓋平面)이 이루는 각도적(角度的) 변화(變化)를 관찰(觀察)하기 위하여 정당교합인(正當咬合人) 남(男) 여(女) 195명(名)의 두부방사선규격사진(頭部放射線規格寫眞)을 Hellma의 치령 분류법(齒齡 分類法)에 의(依)하여 분류(分類)하고 계측(計測) 관찰(觀察)하였든바 다음과 같은 결과(結果)를 얻었다. 1. 성장(成長) 발육기(發育期)에 있어서 전두기저선(前頭基底線)과 His' line이 일정(一定)한 각도(角度) 관계(關係)를 유지한다. 2. His' line은 수평성장축(水平成長軸)으로 생각(生覺)할 수 있다. 3. His' line은 구개평면(口蓋平面)과 대부분(大部分) 일치(一致)하며 남녀(男女)에는 별 차이(差異) 없다. 4. 하악평면(下顎平面)과 His' line이 이루는 각(角)이 심한 것으로 보아 강(强)한 경사도(傾斜度)를 나타내고 있다. 5. 서양인(西洋人)에 비해 하악골(下顎骨)의 후퇴(後退)를 볼 수있다.

• 한국산림과학회지
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• 제85권3호
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• pp.343-346
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• 1996

리기다소나무재의 변색 부위로부터 분리한 변색균을 다시 건전 목재에 접종하여 이 균의 목재 침입경로를 구명한 바, 처음 균사가 목재내 방사유세포에 침입하여 방사유세포 안에서 수평 방향의 이동을 계속하다가, 시간이 경과하면 가도관내로 이동하여 이 가도관을 통로로 하여 수직 방향으로 확산을 계속하였다. 침입 90일이 지나면 목재내 각 조직으로의 침입이 완료되어 균사가 세포내강에 만연한 것을 알 수 있었다. 또한 메탄올 추출물은 변색균의 목재 침입 경로에 영향을 미치지 않는 것으로 분석되었다.

• 대한기계학회논문집
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• 제15권1호
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• pp.299-307
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• 1991

본 연구에서는 근사수평 반류 성층유동에서의 계면마찰계수에 관한 일반화된 실험식을 개발하고자 한다. 이 실험식은 본 저자가 발표한 포화수-수증기와 물-공기 의 실험자료를 기초로 개발되며 공학적인 응용을 위하여 기액상레이놀즈 수와 유체의 물성치를 포함하는 거시적인 유동변수로 표현된다. 또 동일한 계면 마찰계숭에 대한 Nikuradse의 표면조도와 계면의 특성치로 표현되는 무차원 계면 유효조도와의 상관관 계를 구명하고 포화수-수증기와 물-공기의 2상유동에 공통적으로 적용할 수 있는 무차 원 계면유효조도와의 상관관계를 구명하고 포화수-수증기와 물-공기의 2상유동에 공통 적으로 적용할 수 있는 무차원 계면유효조도를 제안할 예정이다. 마지막으로 본 연 구에서 개발한 실험식과 기존 실험식을 비교 검토하고자 한다.

• 한국광학회지
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• 제7권3호
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• pp.191-195
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• 1996

대기오염 연구용 이동형 라이다의 광계통을 설계하였다. 대기오염이나 오종층의 측정을 위해 라이다를 사용하며 군에서는 화생방 오염 측정에도 사용된다. 역 Cassegrain형의 시준기로 평행광을 만들어 평면경에 의해 전송하는 레이저광속과 수신 망원경의 광축이 일치하게 된다. 레이저광속은 대기로 향하여 전송되며 측정하고자 하는 물질에 의해 산란되어 수신 망원경으로 되돌아 온다. 주사반사경은 수직으로 60.deg. 수평으로 180.deg.회전되며 주사한다. 주사반사경은 수신망원경과 분리되어 자동차 지붕위에 설치된다. 수신된 레이저광은 공간주파수 여과기에 의해 여과되고, fabri렌즈에 의해 평행광으로 되어 광속분리기에 의해 2개의 광속으로 나뉘어 검출된다. 각 레이저광은 PM관에 의해 검출되어 증폭되고 분석된다.

• 한국세라믹학회지
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• 제32권4호
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• pp.419-428
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• 1995

Polycrystalline silicon carbide (SiC) thick films were depostied by low pressure chemical vapor deposition (LPCVD) using CH3SiCl3 (MTS) and H2 gaseous mixture onto isotropic graphite substrate. Effects of deposition variables on the SiC film were investigated. Deposition rate had been found to be surface-reaction controlled below reactor temperature of 120$0^{\circ}C$ and mass-transport controlled over 125$0^{\circ}C$. Apparent activation energy value decreased below 120$0^{\circ}C$ and deposition rate decreased above 125$0^{\circ}C$ by depletion effect of the reactant gas in the direction of flow in a horizontal hot wall reactor. Microstructure of the as-deposited SiC films was strongly influenced by deposition temperature and position. Microstructural change occurred greater in the mass transport controlled region than surface reaction controlled region. The as-deposited SiC layers in this experiment showed stoichiometric composition and there were no polytype except for $\beta$-SiC. The preferred orientation plane of the polycrystalline SiC layers was (220) plane at a high reactant gas concentration in the mass transfer controlled region. As depletion effect of reactant concentration was increased, SiC films preferentially grow as (111) plane.

• Journal of Advanced Marine Engineering and Technology
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• 제28권6호
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• pp.922-930
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• 2004

An experimental investigation was performed to study on the generation of air bubble and air core with swirling flow in a horizontal cicular tube. To determine some characteristics of the flow, 2D PIV technique is employed for velocity measurement in water. The experimental rig is manufactured from an acryl tube. The test tube diameter of 80mm, and a length of 3000mm. The used algorithm is the gray leve cross-correlation method(Kimura et al. 1986). An Ar-ion laser is used and the light from the laser(500mW) passes through a probe to make two-dimensional light sheet. In order to make coded images of the tracer particles on one frame, an AOM(Acoustic-Optical Modulator) is used. The maximum axial velocities showed near the test tube wall at y/D =0.1 and y/D =0.9 along the test tube. The higher Reynolds number increase, the lower axial velocities are showed in the center of the test tube. The air bubbles are generated from Re =10,000 and developed into air core from the recirculating water pump rpm equal 30Hz. The pressure and temperature are measured across the test tube at X/D=3.33.

• 한국가시화정보학회지
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• 제1권2호
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• pp.29-37
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• 2003

During the past five decades or so, the characteristics of turbulent swirling flow have been studied extensively because of its great technological and scientific importance. It is well known that the swirling flow improves heat transfer in duct flow. The reason for this is due to the effect of streamline curvature associated with the tangential velocity component. Although many studies have been carried out to investigate the characteristics of the swirling flow in a circular tube. The experimental methods for measuring the velocity components are by hot-wire or LDV (Laser-Doppler-Velocimetry) measuring single point velocity so far. The present study was aimed to analyse the flow characteristics of swirling flow such as time-mean velocity vector, local velocity turbulence intensity and turbulence kinetic energy by using PIV(Particle-Image Velocimetry). The experiment was carried out for four Reynold numbers $1.0\times10^{4}$, $1.5\times10^{4}$, $2.0\times10^{4}$ and $2.5\times10^{4}$ of the measuring area.

• 대한기계학회논문집
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• 제18권5호
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• pp.1264-1274
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• 1994

Heat transfer performance of integral-fin tube which is used in recipro turbo refrigerator or high compact heat exchangers is studied. Eight tubes with trapezoidal shaped integral-fins having fin densities from 748 to 1654 fpm and 10, 30 internal grooves are tested. A plain tube having the same(inner and outer) diameter as the fin tubes is also tested for comparison. Pool boiling heat transfer of R-11 is investigated experimentally and theoretically on single tube arrangement. The refrigerant evaporates at saturation state of 1 bar on the outside tube surface and heat is supplied by not water which circulates inside of the tube. From the result of eight fin tubes and one plain tube tested, a tube having 1299 fpm-30 grooves shows the best performance. A maximum overall heat transfer coefficient of this tube is about 4000 $W/m^{2}K$ at 2.8m/s of water velocity. The maximum heat transfer enhancement (i.e., the ratio of overall heat transfer coefficients of finned to plain tubes)is about 2.1.

• 한국연소학회지
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• 제1권1호
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• pp.19-29
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• 1996

This study is to investigate the characteristics of heat transfer of a horizontal tube, with radial fins of various configuration, immersed in a high temperature fluidized bed. The experimental heat transfer variation is compared with that of a smooth tube. The finned tubes and smooth tube, with outside and inside diameter of 48.6mm and 30.6mm, are made of steel tubes. The depth of the fin is 5mm, the rake angles of fin are $25^{\circ},\;35^{\circ},\;45^{\circ}$ and the widthes of fin for each rake angle are 0mm, 1mm, 2mm and 3mm. A bed temperature is fixed at $880\;{\pm}\;10^{\circ}C$. A granular refractory(silica sand) is used as a bed material with mean particle diameters of 1.22mm and 1.54mm. The maximum heat transfer coefficient is achieved with the rake angle of $25^{\circ}$ and the width of 0mm for the mean particle size 1.22mm. The coefficient is 2.14 times larger than that for a smooth tube. The rake angle for the maximum heat transfer coefficient depends on the particle size of bed material. Also the transfer coefficient decreases as the width of fin increases.